Display surfaces in image display devices such as liquid crystal displays (LCDs), cathode ray tube display devices (CRTs) and plasma display panels (PDPs) are required to reduce the reflection of light emitted from external light sources such as fluorescent lamps to enhance image visibility. Accordingly, based on the phenomenon in which there is a decrease in reflectivity by covering the surface of a transparent object with a transparent film having a low refractive index (low refractive index layer), it has been attempted to increase the image visibility of display surfaces in image display devices by providing an antireflection film thereon to reduce the reflectivity.
There are various methods for obtaining a low refractive index. One of them is a method for decreasing the refractive index of a layer by allowing air having a refractive index of 1 to be contained inside the layer.
As such an air-containing refractive index layer, for example, patent literature 1 disclosed an antireflection film which has a low refractive index layer that comprises an ionizing radiation curable resin composition and a silica fine particle comprising an outer shell layer and an inside that is porous or hollow, wherein at least part of the particle surface is treated with silane coupling agents each comprising an ionizing radiation curable group, with the purpose of providing an antireflection film having a low refractive index and excellent mechanical strength.
With the purpose of increasing the antireflection performance of a low refractive index layer, patent literature 2 disclosed a technique of using a cured film formed from a composition that comprises porous fine particles and a compound having at least two (meth)acryloyloxy groups in a molecule thereof or an oligomer of the compound.
The porous fine particles are inorganic particles, however, so that their affinity with organic binder components is poor if no surface treatment is performed thereon with silane coupling agents or the like. Accordingly, the porous fine particles are likely to be aggregated and unevenly present in the layer formed by curing the composition. As a result, the cured layer is a layer in which the refractive index of the layer surface varies from part to part, or is a layer which has transparent parts and opaque parts together. An antireflection film having such a non-uniform layer structure has a problem of poor abrasion resistance properties such as poor steel wool resistance.
In the hope of increasing the hardness of a refractive index layer and providing the refractive index layer with functions such as an antistatic function, patent literature 3 disclosed a technique of using, as the refractive index layer, a cured layer formed from a composition that comprises porous fine particles, non-porous inorganic compound fine particles, and a binder component selected from curable compounds and resins.
The strength of solid particles is higher than that of hollow particles because the inside of solid particles is neither porous nor hollow, and is densely filled. Accordingly, by incorporating solid particles in the refractive index layer, it is expected to increase the strength of the refractive index layer with respect to pressure in the layer thickness direction (direction perpendicular to the plane of the layer.)
Patent literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2005-99778
Patent literature 2: JP-A No. 2003-262703
Patent literature 3: JP-A No. 2003-266606